Lower olefins (C2-C4 olefins) are the fundamental starting materials for the organic chemical industry, and have an important role in the modern petroleum and chemical industry. As the production process, the technology of using an alkane feedstock to produce light olefins becomes more and more popular. At present, the reactor used in the technology of producing light olefins with an alkane feedstock mainly includes the fixed bed reactor and the fluidized bed reactor. The fixed bed reactor has the disadvantage of the heat transfer effect being poor, the catalyst replacement and regeneration being complex and complicated, the continuous reaction being difficulty conducted, and the like, and the advantage of being capable of achieving a large throughput of an alkane feedstock. In addition, the fluidized bed reactor can solve the aforementioned disadvantage of the fixed bed reactor, but has a much smaller throughput than the fixed bed reactor for the same reactor size as that of the fluidized bed reactor. For example, EP0894781A1 and U.S. Pat. No. 7,235,706B2 disclose processes for producing light olefins by the dehydrogenation of an alkane feedstock, wherein the fluidized bed reactors and the regenerators are used, wherein the reaction temperature is 450-800° C., the reaction pressure is 0.01-0.3 MPa, and the volume space velocity is 100-1000 h−1.
It is known that the reaction producing light olefins with an alkane feedstock is a reaction in which the amount of molecules increases, and therefore the lower reaction pressure is favorable for the chemical equilibrium to proceed toward the production of light olefins. In view of this, in the production of light olefins according to the prior art, a lower reaction pressure is usually used in order to obtain a desired yield of light olefins. This lower reaction pressure (typically 0.1-0.3 MPa) directly results in that if desired to increase the throughput of the alkane feedstock (for example, to achieve the feedstock throughput equivalent to that of the fixed bed in the prior art) in order to increase the output of light olefins, the prior art will therefore have to increase the size or amount of the reactor so as to maintain the yield of light olefins at an acceptable level. Obviously, this will accordingly increase the investment and maintenance cost of the plant.
In the process for producing light olefins according to the prior art, in order to guarantee a continuous production process, the catalyst is circulated between the reactor and the regenerator. In order to facilitate the circulation, the reactor and the regenerator are generally operated at the substantially same pressure. Under this situation, the reactor is in a hydrogen atmosphere (a reducing atmosphere), and the regenerator is in an oxygen-containing atmosphere. If the reactor and the regenerator are not well segregated, there will be a large potential safety hazard.
In addition, a cyclone similar to that used in the catalytic cracking unit is widely used in the plant for producing light olefins according to the prior art. Therefore, it is inevitable for the catalyst natural loss during the production, in particular in case that the catalyst fine powder having a particle size of less than 20 microns becomes more and more in the catalyst. This will have a detrimental effect on the subsequent product separation, and will be adverse for the catalyst to be reused.